158 DRY-FARMING 



ducing evaporation. Fortier, in the experiments in 

 California to wliich allusion has already been made, 

 showed the greater value of deep cultivation. Dur- 

 ing a period of fifteen days, beginning immediately 

 after an irrigation, the soil which had not been 

 mulched lost by evaporation nearly one fourth of 

 the total amount of water that had been added. A 

 mulch 4 inches dee]) saved about 72 per cent of the 

 evaporation ; a mulch 8 inches deep saved about 88 

 per cent, and a mulch 10 inches deep stopped evapo- 

 ration almost wholl}'. It is a most serious mis- 

 take for the dry -farmer, who attempts cultivation 

 for soil-moisture conser^'ation, to fail to get the best 

 results simph' to save a few cents per acre in added 

 labor. 



When to cultivate or till 



It has already been shown that the rate of evap- 

 oration is greater from a wet than from a dr}' surface. 

 It follows, therefore, that the critical time for pre- 

 venting evajjoration is when the soil is wettest. 

 After the soil is tolerably dry, a very large portion 

 of the soil-moisture has been lost, which possibly 

 might have been saved bj' earlier cultivation. The 

 truth of this statement is well sh(n\'n by exjDeriments 

 conducted by the Utah Station. In one case on a soil 

 well filled with water, during a three weeks' period, 

 nearly one half of the total loss occurred the first, 

 while onlv one fifth fell on the third week. Of the 



